Laser working method, laser working apparatus, and its manufacturing method

ABSTRACT

An object is irradiated with a laser light modulated by a reflection type spatial light modulator such that aberration of the laser light converged inside the object becomes a predetermined aberration or less. Therefore, aberration of the laser light generated at a position on which a converging point of the laser light is located is made as small as possible, to enhance the energy density of the laser light at that position, which makes it possible to form a modified region with a high function as a starting point for cutting. In addition, because the reflection type spatial light modulator is used, it is possible to improve the utilization efficiency of the laser light as compared with a transmissive type spatial light modulator.

This is a divisional application of copending application Ser. No.13/362,781, filed on Jan. 31, 2012, which is a continuation applicationof application Ser. No. 12/671,820, filed on Mar. 25, 2010 (now U.S.Pat. No. 8,134,099), which is a national stage application of PCTApplication No. PCT/JP2008/063531 flied on Jul. 28, 2008, designatingthe U.S.A., the entire contents of each of which are incorporated byreference herein in their entirety.

TECHNICAL FIELD

The present invention relates to a laser working method for cutting aplate-shaped object to be processed along a line to cut, a laser workingapparatus and its manufacturing method.

BACKGROUND ART

As a conventional laser working apparatus, in Patent Document 1, thereis described a laser working apparatus that diffuses a laser lightemitted from a laser light source by a laser diffusing point movingmeans, and converges the diffused laser light onto a predeterminedposition inside an object by a converging optical system. In accordancewith the laser working apparatus, it is possible to reduce aberration ofa laser light generated at a predetermined position inside the object.

Note that, in Patent Document 2, there is described a wavefrontcompensating apparatus that modulates a laser light with a spatial lightmodulator, to perform wavefront compensation of the laser light.Further, in Patent Document 3, there is described a laser workingapparatus that modulates a laser light with a spatial light modulator,to converge the laser light onto a plurality of positions inside anobject.

-   Patent Document 1: International Publication Pamphlet No.    2005/106564-   Patent Document 2: Japanese Published Unexamined Patent Application    No. 2005-292662-   Patent Document 3: Japanese Published Unexamined Patent Application    No. 2006-68762

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention

Meanwhile, in a technology of irradiating a plate-shaped object to beprocessed with a laser light while locating a converging point withinthe object, so as to form a modified region along a line to cut, amodified region with a low function as a starting point for cutting (forexample, it is difficult to generate break) depending on a workingcondition such as a distance from a laser light entrance surface of theobject in some cases.

Then, the present invention has been achieved in consideration of suchcircumstances, and an object of the present invention is to provide alaser working method capable of reliably forming a modified regionserving as a starting point for cutting, and a laser working apparatusand its manufacturing method.

Means for Solving the Problems

In order to attain the above-described object, there is provided a laserworking method according to the present invention for irradiating aplate-shaped object to be processed with a laser light while locating aconverging point within the object, so as to form a modified regionserving as a starting point for cutting along a line to cut the object,in the laser working method, at the time of forming the modified region,the laser light is modulated by a reflection type spatial lightmodulator such that a wavefront of the laser light becomes apredetermined wavefront inside the object.

Further, there is provided a laser working method according to thepresent invention for irradiating a plate-shaped object to be processedwith a laser light while locating a converging point within the object,so as to form a modified region serving as a starting point for cuttingalong a line to cut the object, in the laser working method, at the timeof forming the modified region, the laser light is modulated by areflection type spatial light modulator such that aberration of thelaser light converged inside the object becomes a predeterminedaberration or less.

In these laser working methods, the object is irradiated with the laserlight modulated by the reflection type spatial light modulator such thata wavefront of the laser light becomes a predetermined wavefront insidethe object (or, aberration of the laser light converged inside theobject becomes a predetermined aberration or less). Therefore, forexample, aberration of the laser light generated at a position on whicha converging point of the laser light is located is made substantiallyzero, and the energy density of the laser light at that position isenhanced, which makes it possible so as to form a modified region with ahigh function as a starting point for cutting (for example, it is easyto generate break). In addition, because the reflection type spatiallight modulator is used, it is possible to improve the utilizationefficiency of a laser light as compared with a transmissive type spatiallight modulator. Such improvement of the utilization efficiency of alaser light is particularly important in the case in which a modifiedregion serving as a starting point for cutting is formed in aplate-shaped object to be processed. Accordingly, in accordance withthese laser working methods, it is possible to reliably form a modifiedregion serving as a starting point for cutting.

There is provided a laser working method according to the presentinvention for irradiating a plate-shaped object to be processed with alaser light while locating a converging point within the object, to formmodified regions in a plurality of lines serving as starting points forcutting along a line of the object so as to line up in the thicknessdirection of the object, in the laser working method, at the time offorming the modified regions in one line or a plurality of linesincluding a modified region farthest from a laser light entrance surfaceof the object among the modified regions in a plurality of lines, adistance between a converging optical system and the object is changedsuch that a distance between the converging optical system thatconverges the laser light inside the object and the object becomes apredetermined distance in accordance with the modified region to beformed, and the laser light is modulated by a reflection type spatiallight modulator such that a wavefront of the laser light becomes apredetermined wavefront inside the object.

Further, there is provided a laser working method according to thepresent invention for irradiating a plate-shaped object to be processedwith a laser light while locating a converging point within the object,to form modified regions in a plurality of lines serving as startingpoints for cutting along a line to cut the object so as to line up inthe thickness direction of the object, in the laser working method, atthe time of forming the modified regions in one line or a plurality oflines including a modified region farthest from a laser light entrancesurface of the object among the modified regions in a plurality oflines, a distance between a converging optical system and the object ischanged such that a distance between the converging optical system thatconverges the laser light inside the object and the object becomes apredetermined distance in accordance with the modified region to beformed, and the laser light is modulated by a reflection type spatiallight modulator such that aberration of the laser light converged insidethe object becomes a predetermined aberration or less.

In these laser working methods, at the time of forming the modifiedregions in one line or a plurality of lines including a modified regionfarthest from the laser light entrance surface of the object among themodified regions in a plurality of lines, the object is irradiated withthe laser light modulated by the reflection type spatial lightmodulator. The reason for that modulation of the laser light by thereflection type spatial light modulator is required at the time offorming the modified region farthest from the laser light entrancesurface, is because the farther from the laser light entrance surfacethe position at which the modified region is formed is, the larger theaberration of the laser light generated at the position on which theconverging point of the laser light is located is. Accordingly, inaccordance with these laser working methods, it is possible to reliablyform the modified regions serving as starting points for cutting even inthe case in which modified regions in a plurality of lines are formedalong one of the lines.

At this time, in the case in which the plurality of lines are set withrespect to the object, provided that after the modified regions in aplurality of lines are formed along one of the lines, the modifiedregions in a plurality of lines are formed along another one of thelines, the following effect is brought about. That is, in a case wherethere is undulation on the laser light entrance surface of the object,in order to focus the converging point of the laser light on a positionat a predetermined distance from the laser light entrance surface withhigh precision, data on varying levels of the laser light entrancesurface along the line is acquired, to fine-adjust a distance betweenthe converging optical system and the object on the basis of the data onvarying levels. Accordingly, provided that after the modified regions ina plurality of lines are formed along one of the lines, the modifiedregions in a plurality of lines are formed along another one of thelines, it is possible to decrease the number of switching data onvarying levels, and it is possible to form the modified regions in aplurality of lines along the respective lines at positions atpredetermined distances from the laser light entrance surface with highprecision.

Further, in the case in which the plurality of lines are set withrespect to the object, provided that after the modified region in oneline is formed along the plurality of lines, the modified region inanother one line is formed along the plurality of lines, the followingeffect is brought about. That is, in a case where the object breaks bythe formation of the modified regions in a plurality of lines along oneof the lines, if the modified regions in a plurality of lines are formedalong another one of the lines after the modified regions in a pluralityof lines are formed along one of the lines, the position of the objectis shifted by the break of the object. Then, in order to form themodified regions along the lines with high precision, it is necessary tocorrect the position of the object. However, if the modified region inanother one line is formed along a plurality of lines after the modifiedregion in one line is formed along the plurality of lines, it ispossible to prevent the position of the object from being shifted by thebreak of the object, and the number of corrections for the position ofthe object is decreased, which makes it possible to form the modifiedregions in a plurality of lines along the plurality of lines in a shorttime.

There is provided a laser working method according to the presentinvention for irradiating a plate-shaped object to be processed with alaser light while locating a converging point within the object, so asto form a modified region serving as a starting point for cutting alonga line to cut the object, in the laser working method, at the time offorming the modified region, the laser light is modulated by areflection type spatial light modulator such that a numerical apertureof the laser light converged inside the object becomes a predeterminednumerical aperture.

In this laser working method, the object is irradiated with the laserlight modulated by the reflection type spatial light modulator such thata numerical aperture of the laser light converged inside the objectbecomes a predetermined numerical aperture. Therefore, for example, themodified region with a high function as a starting point for cutting canbe formed by changing the numerical aperture of the laser lightaccording to a material of the object, a distance to a position at whichthe modified region must be formed, or the like.

There is provided a laser working method according to the presentinvention for irradiating a plate-shaped object to be processed with alaser light while locating a converging point within the object, to formmodified regions in a plurality of lines serving as starting points forcutting along a line to cut the object so as to line up in the thicknessdirection of the object, in the laser working method, at the time offorming the modified regions except for the modified region closest to alaser light entrance surface of the object or an opposed surface opposedto the laser light entrance surface in the object among the modifiedregions in a plurality of lines, the laser light is modulated by areflection type spatial light modulator such that a numerical apertureof the laser light converged inside the object is made smaller ascompared with the case in which the modified region closest to the laserlight entrance surface or the opposed surface is formed.

In this laser working method, at the time of forming the modified regionclosest to the laser light entrance surface of the object or the opposedsurface opposed to the laser light entrance surface in the object, as amodified region particularly important as a starting point for cutting,the object is irradiated with the laser light modulated by thereflection type spatial light modulator such that a numerical apertureof the laser light converged inside the object is made larger ascompared with the case in which the other modified regions are formed.Therefore, the modified region closest to the laser light entrancesurface of the object or the opposed surface opposed to the laser lightentrance surface in the object can be made to be a modified region withan extremely high function as a starting point for cutting (for example,a modified region including break).

At this time, in the case in which the modified regions are formed in atleast three lines along the line so as to line up in the thicknessdirection of the object, at the time of forming the modified regionsexcept for the modified region farthest from the laser light entrancesurface and the modified region closest to the laser light entrancesurface among the modified regions in at least three lines, the laserlight is preferably modulated by the reflection type spatial lightmodulator such that a numerical aperture of the laser light convergedinside the object is made smaller as compared with the case in which themodified region farthest from the laser light entrance surface and themodified region closest to the laser light entrance surface are formed.In this case, at the time of forming the modified region farthest fromthe laser light entrance surface and the modified region closest to thelaser light entrance surface as the modified regions particularlyimportant as starting points for cutting, the object is irradiated withthe laser light modulated by the reflection type spatial light modulatorsuch that a numerical aperture of the laser light converged inside theobject is made larger as compared with the case in which the modifiedregion therebetween is formed. Therefore, the modified region farthestfrom the laser light entrance surface and the modified region closest tothe laser light entrance surface can be made to be the modified regionswith extremely high functions as starting points for cutting (forexample, modified regions including break).

There is provided a laser working method according to the presentinvention for irradiating a plate-shaped object to be processed with alaser light while locating a converging point within the object, so asto form a modified region serving as a starting point for cutting alonga line to cut the object, in the laser working method, at the time offorming the modified region, the laser light is modulated by a pluralityof reflection type spatial light modulators such that an opticalcharacteristic of the laser light becomes a predetermined opticalcharacteristic.

In this laser working method, the object is irradiated with the laserlight modulated by the plurality of reflection type spatial lightmodulators such that an optical characteristic of the laser lightbecomes a predetermined optical characteristic. In this way, when aplurality of reflection type spatial light modulators are used, it ispossible to control its beam diameter, its optical axis, or the like asan optical characteristic of the laser light. Thereby, it is possible toreliably form the modified region serving as a starting point forcutting.

There is provided a laser working apparatus according to the presentinvention, that irradiates a plate-shaped object to be processed with alaser light while locating a converging point within the object, so asto form a modified region serving as a starting point for cutting alonga line to cut the object, the laser working apparatus includes asupporting base supporting the object, a laser light source emitting thelaser light, a reflection type spatial light modulator modulating thelaser light emitted from the laser light source, a converging opticalsystem converging the laser light modulated by the reflection typespatial light modulator, inside the object supported by the supportingbase, and a controller that, at the time of forming the modified region,controls at least one of the supporting base and the converging opticalsystem such that a converging point of the laser light is located at apredetermined distance from a laser light entrance surface of the objectand the converging point of the laser light is relatively moved alongthe line, and controls the reflection type spatial light modulator suchthat a wavefront of the laser light becomes a predetermined wavefrontinside the object.

In accordance with this laser working apparatus, it is possible toirradiate the object with the laser light modulated by the reflectiontype spatial light modulator such that a wavefront of the laser lightbecomes a predetermined wavefront inside the object, along the line.Thereby, it is possible to reliably form the modified region serving asa starting point for cutting. Note that the term “the controllercontrolling at least one of the supporting base and the convergingoptical system” includes not only the case in which the controllerdirectly controls at least one of the supporting base and the convergingoptical system, but also the case in which the controller directlycontrols at least one of a system including the supporting base and asystem including the converging optical system, to indirectly control atleast one of the supporting base and the converging optical system.

At this time, the controller preferably stores a control signal forcontrolling at least one of the supporting base and the convergingoptical system such that a converging point of the laser light islocated at a predetermined distance from the laser light entrancesurface for each of the modified regions formed in a plurality of linesalong the line so as to line up in the thickness direction of theobject, and a control signal for controlling the reflection type spatiallight modulator such that a wavefront of the laser light becomes apredetermined wavefront inside the object so as to associate the controlsignals with each other therein. In this case, a wavefront of the laserlight can be made to be a predetermined wavefront inside the object inaccordance with each of the modified regions in a plurality of lines tobe formed.

There is provided a laser working apparatus according to the presentinvention that irradiates a plate-shaped object to be processed with alaser light while locating a converging point within the object, so asto form a modified region serving as a starting point for cutting alonga line to cut the object, the laser working apparatus including: asupporting base supporting the object, a laser light source emitting thelaser light, a reflection type spatial light modulator modulating thelaser light emitted from the laser light source, a converging opticalsystem converging the laser light modulated by the reflection typespatial light modulator, inside the object supported by the supportingbase, and a controller that, at the time of forming the modified region,controls at least one of the supporting base and the converging opticalsystem such that a converging point of the laser light is located at apredetermined distance from a laser light entrance surface of the objectand the converging point of the laser light is relatively moved alongthe line, and controls the reflection type spatial light modulator suchthat aberration of the laser light converged inside the object becomes apredetermined aberration or less.

In accordance with this laser working apparatus, it is possible toirradiate the object with the laser light modulated by the reflectiontype spatial light modulator such that aberration of the laser lightconverged inside the object becomes a predetermined aberration or less,along the line. Thereby, it is possible to reliably form the modifiedregion serving as a starting point for cutting.

At this time, the controller preferably stores a control signal forcontrolling at least one of the supporting base and the convergingoptical system such that a converging point of the laser light islocated at a predetermined distance from the laser light entrancesurface for each of the modified regions formed in a plurality of linesalong the line so as to line up in the thickness direction of theobject, and a control signal for controlling the reflection type spatiallight modulator such that aberration of the laser light converged insidethe object becomes a predetermined aberration or less so as to associatethe control signals with each other therein. In this case, aberration ofthe laser light converged inside the object can be made to be apredetermined aberration or less in accordance with each of the modifiedregions in a plurality of lines to be formed.

There is provided a laser working apparatus according to the presentinvention that irradiates a plate-shaped object to be processed with alaser light while locating a converging point within the object, so asto form a modified region serving as a starting point for cutting alonga line to cut the object, the laser working apparatus including: asupporting base supporting the object, a laser light source emitting thelaser light, a plurality of reflection type spatial light modulatorsmodulating the laser light emitted from the laser light source, aconverging optical system converging the laser light modulated by thereflection type spatial light modulator, inside the object supported bythe supporting base, and a controller that, at the time of forming themodified region, controls at least one of the supporting base and theconverging optical system such that a converging point of the laserlight is located at a predetermined distance from a laser light entrancesurface of the object and the converging point of the laser light isrelatively moved along the line, in which the controller has a functionof controlling the reflection type spatial light modulator such that anoptical characteristic of the laser light becomes a predeterminedoptical characteristic.

In accordance with this laser working apparatus, because the pluralityof reflection type spatial light modulators are provided, it is possibleto control its beam diameter, its optical axis, or the like as anoptical characteristic of the laser light. Accordingly, even in the casein which the optical axis of the laser light is shifted from any cause,it is possible to easily correct the shift, to reliably form themodified region serving as a starting point for cutting.

There is provided a manufacturing method of a laser working apparatusaccording to the present invention, the laser working apparatus whichincludes a supporting base supporting a plate-shaped object to beprocessed, a laser light source emitting a laser light, a reflectiontype spatial light modulator modulating the laser light emitted from thelaser light source, a converging optical system converging the laserlight modulated by the reflection type spatial light modulator, insidethe object supported by the supporting base, and a controllercontrolling the reflection type spatial light modulator, and thatirradiates the object with the laser light while locating a convergingpoint within the object, so as to form a modified region serving as astarting point for cutting along a line to cut the object, themanufacturing method of the laser working apparatus including the stepof: preparing a standard laser working apparatus and acquiring standardwavefront data by measuring a wavefront of a standard laser lightemitted from a standard converging optical system of the standard laserworking apparatus, acquiring wavefront data by measuring a wavefront ofthe laser light emitted from the converging optical system, andcalculating a control signal for controlling the reflection type spatiallight modulator such that the wavefront of the laser light becomes thewavefront of the standard laser light on the basis of the standardwavefront data and the wavefront data, to store the control signal inthe controller.

In accordance with this manufacturing method of the laser workingapparatus, by preparing the laser working apparatus capable of formingthe modified region with a high function as a starting point for cuttingas the standard laser working apparatus, it is possible to make up anindividual difference between the apparatuses, and to manufacture thelaser working apparatus having the performance equivalent to that of thestandard laser working apparatus.

Effect of the Invention

In accordance with the present invention, it is possible to reliablyform a modified region serving as a starting point for cutting.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic block diagram of a laser working apparatus usedfor forming a modified region.

FIG. 2 is a plan view of an object targeted to form a modified regiontherein.

FIG. 3 is a cross-sectional view along the line III-III of the object ofFIG. 2.

FIG. 4 is a plan view of the object after laser working.

FIG. 5 is a cross-sectional view along the line V-V of the object ofFIG. 4.

FIG. 6 is a cross-sectional view along the line VI-VI of the object ofFIG. 4.

FIG. 7 is a view showing a photograph of a cutting plane of a siliconwafer after laser working.

FIG. 8 is a graph showing the relationship between the wavelengths of alaser light and the transmittances inside a silicon substrate.

FIG. 9 is a graph showing the relationship between the peak powerdensities of a laser light and the sizes of crack spots.

FIG. 10 is a schematic block diagram of a laser working apparatusaccording to the present embodiment.

FIG. 11 is an exploded perspective view of a reflection type spatiallight modulator of the laser working apparatus of FIG. 10.

FIG. 12 is a schematic block diagram of a standard laser workingapparatus used for a manufacturing method of the laser working apparatusaccording to the present embodiment.

FIG. 13 is a schematic block diagram of the laser working apparatus usedfor the manufacturing method of the laser working apparatus according tothe present embodiment.

FIG. 14 is a schematic block diagram of the laser working apparatus usedfor the manufacturing method of the laser working apparatus according tothe present embodiment.

FIG. 15 is a schematic block diagram of the laser working apparatus usedfor the manufacturing method of the laser working apparatus according tothe present embodiment.

FIG. 16 is a plan view of an object targeted for a laser working methodaccording to the present embodiment.

FIG. 17 is a cross-sectional view of the object of FIG. 16 onto whichthe laser working method according to the present embodiment is carriedout.

FIG. 18 is a cross-sectional view of the object of FIG. 16 onto whichthe laser working method according to the present embodiment is carriedout.

FIG. 19 is a schematic block diagram of another laser working apparatusaccording to the present embodiment.

FIG. 20 is an explanatory diagram of the disposition of a reflectiontype spatial light modulator of the laser working apparatus of FIG. 19.

FIG. 21 is an explanatory diagram of another laser working methodaccording to the present embodiment.

FIG. 22 is an explanatory diagram of the other laser working methodaccording to the present embodiment.

FIG. 23 is a schematic block diagram of another laser working apparatusaccording to the present embodiment.

FIG. 24 is a schematic block diagram of another standard laser workingapparatus used for the manufacturing method of the laser workingapparatus according to the present embodiment.

FIG. 25 is a schematic block diagram of another laser working apparatusused for the manufacturing method of the laser working apparatusaccording to the present embodiment.

FIG. 26 is a schematic block diagram of yet another laser workingapparatus used for the manufacturing method of the laser workingapparatus according to the present embodiment.

FIG. 27 is a schematic block diagram of yet another laser workingapparatus used for the manufacturing method of the laser workingapparatus according to the present embodiment.

FIG. 28 is a schematic block diagram of another laser working apparatusaccording to the present embodiment.

FIG. 29 is a schematic block diagram of yet another laser workingapparatus according to the present embodiment.

DESCRIPTION OF SYMBOLS

1: Object to be processed, 3: Front face (laser light entrance surface),5: Line to cut, 7, 7 ₁ to 7 ₄: Modified regions, 200: Laser workingapparatus, 200 s: Standard laser working apparatus, 201: Supportingbase, 202: Laser light source, 203: Reflection type spatial lightmodulator, 204: Converging optical system, 204 s: Standard convergingoptical system, 205: Controller, L: Laser light, Ls: Standard laserlight, P: Converging point.

BEST MODES FOR CARRYING OUT THE INVENTION

Hereinafter, a preferred embodiment of the present invention will bedescribed in detail with reference to the drawings. Note that the sameor corresponding portions in the respective drawings are denoted by thesame reference numerals and letters, and overlapping descriptionsthereof will be omitted.

In a laser working method and a laser working apparatus according to thepresent embodiment, a plate-shaped object to be processed is irradiatedwith a laser light while locating a converging point on the object, soas to form a modified region in the object along a line to cut.

Then, first, the formation of a modified region in the laser workingmethod and the laser working apparatus according to the presentembodiment will be described with reference to FIGS. 1 to 9.

As shown in FIG. 1, a laser working apparatus 100 is equipped with alaser light source 101 that performs pulsed oscillation of a laser light(laser light for working) L, a dichroic mirror 103 which is disposed soas to change the optical axis of the laser light L in direction by 90degrees, and a converging lens 105 for converging the laser light L.Further, the laser working apparatus 100 is equipped with a supportingbase 107 for supporting an object to be processed 1 irradiated with thelaser light L converged by the converging lens 105, a stage 111 formoving the supporting base 107 in the X-, Y-, and Z-axis directions, alaser light source controller 102 that controls the laser light source101 in order to adjust an output, a pulse width, and the like of thelaser light L, and a stage controller 115 that controls the movement ofthe stage 111.

In this laser working apparatus 100, the laser light L emitted from thelaser light source 101 is changed in direction of its optical axis by 90degrees by the dichroic mirror 103, and is converged inside the object 1placed on the supporting base 107 by the converging lens 105. At thesame time, the stage 111 is moved, to relatively move the object 1 alonga line to cut 5 with respect to the laser light L. Thereby, a modifiedregion serving as a starting point for cutting is to be formed in theobject 1 along the line 5. Hereinafter, this modified region will bedescribed in detail.

As shown in FIG. 2, the line 5 for cutting the object 1 is set on theplate-shaped object 1. The line 5 is a linearly-extended virtual line.In the case in which a modified region is formed inside the object 1, asshown in FIG. 3, the laser light L is relatively moved along the line 5(i.e., in the direction of arrow A in FIG. 2) in a state in which aconverging point P is located on the inside of the object 1. Thereby, asshown in FIGS. 4 to 6, a modified region 7 is formed inside the object 1along the line 5, and the modified region 7 formed along the line 5serves as a starting point region for cutting region 8.

Note that the converging point P is a place on which the laser light Lis converged. Further, the line 5 is not limited to a linear shape, andmay be a curved shape, and is not limited to a virtual line, and may bea line actually drawn on a front face 3 of the object 1. Further, themodified region 7 is continuously formed in some cases, and isintermittently formed in some cases. Further, it suffices that themodified region 7 is formed at least inside the object 1. Further,crevices are formed from the modified region 7 as a starting point insome cases, and crevices and the modified region 7 may be exposed to theouter surface (the front face, the rear face, or the outercircumferential face) of the object 1.

Incidentally, here, the laser light L is made transmissive through theobject 1 and is absorbed particularly in the vicinity of the convergingpoint inside the object 1, and thereby forming the modified region 7 inthe object 1 (i.e., internal absorption type laser working). Therefore,the laser light L is hardly absorbed into the front face 3 of the object1, and thus, the front face 3 of the object 1 does not melt in any case.Generally, in the case in which removal portions such as holes, grooves,and the like are melted and removed from the front face 3 to be formed(surface absorption type laser working), a working region graduallyadvances from the front face 3 side to the rear face side.

Meanwhile, a modified region formed by the laser working method and thelaser working apparatus according to the present embodiment means aregion coming into a state different in its density, refractive index,mechanical strength, and other physical characteristics from thecircumference thereof. For example, there is a (1) molten processedregion, (2) crack region, dielectric breakdown region, (3) refractiveindex changed region, and the like, and there are also regions wherethese are mixed.

A modified region by the laser working method and the laser workingapparatus according to the present embodiment is formed by a phenomenonsuch as local absorption or multiple photon absorption of a laser light.When the energy hν of photons is less than the bandgap E_(G) ofabsorption of a material, the material is made optically-transparent,which leads to the condition of hν>E_(G) under which absorption occursin the material. The multiple photon absorption means a phenomenon that,even if a material is optically-transparent, absorption occurs in thematerial under the condition of nhν>E_(G) (n=2, 3, 4, and . . . ) bymaking the intensity of the laser light L extremely high. The formationof a molten processed region by multiple photon absorption is describedin, for example, “Ultrashort Pulse Laser Microprocessing of Silicon” onpages 72 to 73 in Pre-Prints of the National Meeting of JWS (JapanWelding Society) 66 (April, 2000).

Further, as described in D. Du, X. Liu, G. Korn, J. Squier, and G.Mourou, “Laser Induced Breakdown by Impact Ionization in SiO₂ with PulseWidths from 7 ns to 150 fs,” Appl Phys Lett 64 (23), Jun. 6, 1994, amodified region formed by utilizing an ultrashort pulse laser light witha pulse width from several picoseconds to femtoseconds may be utilized.

(1) In the Case of a Modified Region Including a Molten Processed Region

An object (for example, a semiconductor material such as silicon) isirradiated with the laser light L under the condition that the electricfield intensity at a converging point is 1×10⁸ (W/cm²) or more and itspulse width is 1 μs or less while locating the converging point withinthe object. Thereby, the laser light L is absorbed in the vicinity ofthe converging point to locally heat the inside of the object, and amolten processed region is formed inside the object by the heating.

A molten processed region is a region which is once melted and againsolidified after that, a region in a currently melt state, or a regionin a state of being again solidified from a melt state, or may be calleda phase-changed region or a region whose crystalline structure ischanged. Further, a molten processed region may be called a region whosecertain structure is changed to another structure in a singlecrystalline structure, an amorphous structure, or a polycrystallinestructure. That is, for example, a molten processed region means aregion changed to an amorphous structure from its single crystallinestructure, a region changed to a polycrystalline structure from itssingle crystalline structure, and a region changed to a structureincluding an amorphous structure and a polycrystalline structure fromits single crystalline structure. In the case in which an object has asilicon single crystalline structure, a molten processed region has anamorphous silicon structure, for example.

FIG. 7 is a view showing a photograph of a cross section of one part ofa silicon wafer (semiconductor substrate) irradiated with a laser light.As shown in FIG. 7, a molten processed region 13 is formed inside asemiconductor substrate 11.

It will be described that the molten processed region 13 is formedinside a material which is transmissive for a wavelength of a laserlight incident thereon. FIG. 8 is a diagrammatic view showing therelationship between wavelengths of a laser light and transmittancesinside silicon substrates. However, the respective reflection componentson the front face sides and the rear face sides of the siliconsubstrates are removed, and only the transmittances inside the siliconsubstrates are shown. The above-described relationships of therespective silicon substrates with thicknesses of 50 μm, 100 μm, 200 μm,500 μm, and 1000 μm are shown.

For example, it is understood that, in the case in which the thicknessof the silicon substrate is 500 μm or less at 1064 nm which is thewavelength of an Nd:YAG laser, 80% or more of the laser light L is madetransmissive inside the silicon substrate. Because the thickness of thesemiconductor substrate 11 shown in FIG. 7 is 350 μm, the moltenprocessed region 13 is formed in the vicinity of the center of thesemiconductor substrate 11, i.e., in the portion 175 μm from the frontface. Because the transmittance in this case is 90% or more withreference to a silicon wafer with a thickness of 200 μm, the laser lightL is absorbed in a slight quantity inside the semiconductor substrate11, and most of the laser light L is made transmissive through thesemiconductor substrate 11. However, the laser light L is convergedinside the silicon wafer under the condition that the peak power densityis 1×10⁸ (W/cm²) or more and its pulse width is 1 μs or less, to causethe laser light to be locally absorbed in the converging point and thevicinity thereof, thereby forming the molten processed region 13 insidethe semiconductor substrate 11.

Note that crevices may be generated from a molten processed region as astarting point in a silicon wafer in some cases. Further, a moltenprocessed region may be formed so as to contain crevices in some cases.In this case, the cracks may be formed over the entire surface in themolten processed region, or may be formed only in one portion or in aplurality of portions. Moreover, the crevices may grow naturally in somecases, or may grow by applying force to the silicon wafer in some cases.In the case in which the crevices grow naturally from a molten processedregion, there are both the case in which the cracks grow from a state inwhich the molten processed region is melted, and the case in which thecracks grow when the molten processed region is again solidified from astate in which the molten processed region is melted. However, in any ofthe cases, the molten processed region is formed inside the siliconwafer, and on its cutting plane, the molten processed region is formedinside the silicon wafer as shown in FIG. 7.

(2) In the Case of a Modified Region Including a Crack Region

An object (for example, glass or a piezoelectric material formed ofLiTaO₃) is irradiated with the laser light L under the condition thatthe electric field intensity at a converging point is 1×10⁸ (W/cm²) ormore and its pulse width is 1 μs or less while locating the convergingpoint within the object. This size of a pulse width is the conditionunder which the laser light L is absorbed into the inside of the objectto form a crack region. Thereby, a phenomenon called optical damageinside the object occurs. Thermal strain is induced inside the object bythe optical damage, thereby a crack region including one or a pluralityof cracks are formed inside the object. A crack region may also becalled a dielectric breakdown region.

FIG. 9 is a diagrammatic view showing the experimental results of therelationship between electric field intensities and sizes of cracks.Peak power densities are plotted on the abscissa, and because the laserlight L is a pulse laser light, its electric field intensities areexpressed by the peak power densities. The sizes of cracked portions(crack spots) formed inside the object by the laser light L of one pulseare plotted on the ordinate. Crack spots gather to become a crackregion. The sizes of crack spots are sizes of portions having themaximum lengths in the shapes of the crack spots. The data shown byblack circles in the graph is in the case in which the magnification ofthe converging lens (C) is 100-times and the numerical aperture (NA)thereof is 0.80. On the other hand, the data shown by white circles inthe graph is in the case in which the magnification of the converginglens (C) is 50-times and the numerical aperture (NA) thereof is 0.55. Itis understood that the crack spots are generated inside the object fromwhen the peak power density is approximately 10¹¹ (W/cm²), and crackspots become greater as the peak power density is increased.

(3) In the Case of a Modified Region Including a Refractive IndexChanged Region

An object (for example, glass) is irradiated with the laser light Lunder the condition that the electric field intensity at a convergingpoint is 1×10⁸ (W/cm²) or more and its pulse width is 1 μs or less whilelocating the converging point within the object. In this way, when thelaser light L is absorbed into the inside of the object in a state inwhich its pulse width is extremely short, the energy thereof is nottransformed into thermal energy, and permanent structural changes suchas ionic valence change, crystallization, polarization orientation, orthe like are induced inside the object, which forms a refractive indexchanged region.

Note that a modified region including a molten processed region, adielectric breakdown region, a refractive index changed region, or aregion in which these are mixed, may be a region in which the density ofa modified region is changed as compared with the density of anunmodified region in its material, or may be a region in which a latticedefect is formed. These may also be collectively called a high-densitytransfer region.

Further, in some cases, a molten processed region, a refractive indexchanged region, a region in which the density of a modified region ischanged as compared with the density of an unmodified region, and aregion in which a lattice defect is formed may further contain crevices(break, microcracks) inside those regions or in the interface betweenthe modified region and the unmodified region. Crevices to be containedmay spread over the entire surface of the modified region or are formedin only one portion or a plurality of portions in some cases.

Incidentally, provided that a modified region is formed as follows inconsideration of the crystalline structure or the cleavability of theobject, it is possible to cut the object with high precision.

That is, in the case of a substrate formed of a single crystallinesemiconductor such as silicon having a diamond structure, a modifiedregion is preferably formed in a direction along the (111) plane (firstcleavage plane) or the (110) plane (second cleavage plane). Further, inthe case of a substrate formed of a III-V group compound semiconductorhaving a zinc blende structure such as GaAs, a modified region ispreferably formed in a direction along the (110) plane. Moreover, in thecase of a substrate having a hexagonal crystalline structure such assapphire (Al₂O₃), a modified region is preferably formed in a directionalong the (1120) plane (A-plane) or the (1100) plane (M-plane) with the(0001) plane (C-plane) being as a principal plane.

Further, provided that an orientation flat is formed on the substratealong the direction in which a modified region must be formed (forexample, a direction along the (111) plane in the single crystallinesilicon substrate) described above, or a direction perpendicular to adirection in which the modified region must be formed, it is possible toeasily and accurately form a modified region on the substrate by use ofthe orientation flat as a standard.

Next, the laser working apparatus according to the present embodimentwill be described.

As shown in FIG. 10, the laser working apparatus 200 is equipped with asupporting base 201 that supports the plate-shaped object 1, a laserlight source 202 that emits the laser light L, a reflection type spatiallight modulator 203 that modulates the laser light L emitted from thelaser light source 202, a converging optical system 204 that convergesthe laser light L modulated by the reflection type spatial lightmodulator 203 inside the object 1 supported by the supporting base 201,and a controller 205 that controls the reflection type spatial lightmodulator 203. The laser working apparatus 200 is configured toirradiate the object 1 with the laser light L while locating theconverging point P within the object 1, to form the modified region 7serving as a starting point for cutting along the line 5 of the object1.

The reflection type spatial light modulator 203 is installed in a case231, and the laser light source 202 is installed on the top panel of thecase 231. Further, the converging optical system 204 is composed of aplurality of lenses, and is installed on the bottom panel of the case231 via a driving unit 232 composed of a piezoelectric element and thelike. Then, a laser engine 230 is composed of the parts installed in thecase 231. Note that the controller 205 may be installed in the case 231of the laser engine 230.

A movement mechanism (not shown) that moves the case 231 in thethickness direction of the object 1 is installed in the case 231.Thereby, it is possible to move the laser engine 230 up and downaccording to a depth of the object 1, which enables to change a positionof the converging optical system 204 to converge the laser light L on adesired depth position of the object 1. Note that, in place ofinstallation of the movement mechanism in the case 231, a movementmechanism that moves the supporting base 201 in the thickness directionof the object 1 may be provided to the supporting base 201. Further, theconverging optical system 204 may be moved in the thickness direction ofthe object 1 by utilizing an AF unit 212 which will be described later.Then, these may be combined.

The controller 205 not only controls the reflection type spatial lightmodulator 203, but also controls the entire laser working apparatus 200.For example, at the time of forming the modified region 7, thecontroller 205 controls the laser engine 230 including the convergingoptical system 204 such that the converging point P of the laser light Lis located at a predetermined distance from the front face (laser lightentrance surface) 3 of the object 1 and the converging point P of thelaser light L relatively moves along the line 5. Note that, in order torelatively move the converging point P of the laser light L with respectto the object 1, the controller 205 may control, not the laser engine230 including the converging optical system 204, but the supporting base201, or may control both the laser engine 230 including the convergingoptical system 204 and the supporting base 201.

The laser light L emitted from the laser light source 202 is reflectedin sequence by mirrors 206 and 207 in the case 231, and thereafter, thelaser light L is reflected by a reflective member 208 such as a prism tobe made incident onto the reflection type spatial light modulator 203.The laser light L incident onto the reflection type spatial lightmodulator 203 is modulated by the reflection type spatial lightmodulator 203, to be emitted from the reflection type spatial lightmodulator 203. The laser light L emitted from the reflection typespatial light modulator 203 is reflected by the reflective member 208 soas to be along the optical axis of the converging optical system 204 inthe case 231, and the laser light L is made transmissive in sequencethrough beam splitters 209 and 210 to be made incident onto theconverging optical system 204. The laser light L incident onto theconverging optical system 204 is converged inside the object 1 placed onthe supporting base 201 by the converging optical system 204.

Further, the laser working apparatus 200 is equipped with a surfaceobserving unit 211 for observing the front face 3 of the object 1 in thecase 231. The surface observing unit 211 emits a visible light VL whichis reflected by the beam splitter 209 to be made transmissive throughthe beam splitter 210, and detects the visible light VL which isconverged by the converging optical system 204 to be reflected by thefront face 3 of the object 1, to acquire an image of the front face 3 ofthe object 1.

Moreover, the laser working apparatus 200 is equipped with the AF(auto-focus) unit 212 for focusing the converging point P of the laserlight L on a position at a predetermined distance from the front face 3with high precision even in a case where there is undulation on thefront face 3 of the object 1, in the case 231. The AF unit 212 emits alaser light for auto-focus LB reflected by the beams splitter 210, anddetects the laser light for auto-focus LB which is converged by theconverging optical system 204 to be reflected by the front face 3 of theobject 1, to acquire data on varying levels of the front face 3 alongthe line 5 by use of, for example, an astigmatic method. Then, at thetime of forming the modified region 7, the AF unit 212 causes thedriving unit 232 to drive on the basis of the acquired data on varyinglevels, to move the converging optical system 204 to reciprocate in itsoptical axis direction so as to be along the undulation of the frontface 3 of the object 1, that fine-adjusts a distance between theconverging optical system 204 and the object 1.

Here, the reflection type spatial light modulator 203 will be described.As shown in FIG. 11, the reflection type spatial light modulator 203 isequipped with a silicon substrate 213, a metal electrode layer 214provided on the silicon substrate 213, a mirror layer 215 provided onthe metal electrode layer 214, a liquid crystal layer 216 provided onthe mirror layer 215, a transparent electrode layer 217 provided on theliquid crystal layer 216, and a glass plate 218 provided on thetransparent electrode layer 217. The metal electrode layer 214 and thetransparent electrode layer 217 have a plurality of electrode sections214 a and 217 a arranged in a matrix state, and the respective electrodesections 214 a of the metal electrode layer 214 and the respectiveelectrode sections 217 a of the transparent electrode layer 217 faceeach other in the laminating direction of the reflection type spatiallight modulator 203.

In the reflection type spatial light modulator 203 configured asdescribed above, the laser light L is made transmissive in sequencethrough the glass plate 218 and the transparent electrode layer 217 fromthe outside, to be made incident onto the liquid crystal layer 216, andthe laser light L is reflected by the mirror layer 215 to be madetransmissive in sequence through the transparent electrode layer 217 andthe glass plate 218 from the liquid crystal layer 216, to be emitted tothe outside. At this time, a voltage is applied to each pair of theelectrode sections 214 a and 217 a facing each other, and a refractiveindex of a portion sandwiched by the pair of electrode sections 214 aand 217 a facing each other in the liquid crystal layer 216 is changedaccording to its voltage. Thereby, shifts in phases of components in apredetermined direction perpendicular to a traveling direction ofrespective rays in the plurality of respective rays composing the laserlight L, is caused to shape (phase-modulate) the laser light L.

At the time of forming the modified region 7, the controller 205 appliesa voltage to each pair of the electrode sections 214 a and 217 a facingeach other to control the reflection type spatial light modulator 203such that aberration of the laser light L converged inside the object 1becomes a predetermined aberration or less (in other words, thewavefront of the laser light L becomes a predetermined wavefront insidethe object 1). The controller 205 inputs wavefront shaping (aberrationcorrection) pattern information for shaping (modulating) a beam pattern(beam wavefront) of the laser light L incident onto the reflection typespatial light modulator 203 to the reflection type spatial lightmodulator 203. Then, a refractive index of the liquid crystal layer 216corresponding to each pair of the electrode sections 214 a and 217 a ofthe reflection type spatial light modulator 203 is changed by a signalbased on the input pattern information, to shape (modulate) the beampattern (beam wavefront) of the laser light L emitted from thereflection type spatial light modulator 203. Note that patterninformation to be input to the reflection type spatial light modulator203 may be input serially thereto or pattern information stored inadvance may be selected to be input thereto.

Meanwhile, strictly speaking, the laser light L modulated (corrected) bythe reflection type spatial light modulator 203 is changed in itswavefront form due to its propagation through space. In particular, inthe case in which the laser light L emitted from the reflection typespatial light modulator 203 or the laser light L incident onto theconverging optical system 204 is a light having a predetermined spread(i.e., a light other than a parallel light), the wavefront form at thereflection type spatial light modulator 203 and the wavefront form atthe converging optical system 204 do not match one another, and as aresult, precise internal working to be targeted may be interrupted.Therefore, it is important to match the wavefront form at the reflectiontype spatial light modulator 203 to the wavefront form at the convergingoptical system 204. For that purpose, it is more desirable that a changein its wavefront form when the laser light L propagates from thereflection type spatial light modulator 203 to the converging opticalsystem 204 is determined by measurement or the like, and wavefrontshaping (aberration correction) pattern information taking into accountthe change in the wavefront form is input to the reflection type spatiallight modulator 203.

Or, in order to match the wavefront form at the reflection type spatiallight modulator 203 to the wavefront form at the converging opticalsystem 204, as shown in FIG. 23, an adjustment optical system 240 may beprovided on the optical path of the laser light L traveling between thereflection type spatial light modulator 203 and the converging opticalsystem 204. Thereby, it is possible to accurately achieve wavefrontshaping.

The adjustment optical system 240 has at least two lenses of a lens(first optical element) 241 a and a lens (second optical element) 241 b.The lenses 241 a and 241 b are for matching the wavefront form at thereflection type spatial light modulator 203 to the wavefront form at theconverging optical system 204 in similarity. The lenses 241 a and 241 bare disposed between the reflection type spatial light modulator 203 andthe reflective member 208 such that a distance between the reflectiontype spatial light modulator 203 and the lens 241 a becomes a focallength (first focal length) f1 of the lens 241 a, a distance between theconverging optical system 204 and the lens 241 b becomes a focal length(second focal length) f2 of the lens 241 b, a distance between the lens241 a and the lens 241 b becomes f1+f2, and the lens 241 a and the lens241 b becomes a double telecentric optical system.

By disposing the lenses 241 a and 241 b in this way, even if the laserlight L has a small spread angle of approximately 1 degree or less, itis possible to align the wavefront at the reflection type spatial lightmodulator 203 to the wavefront at the converging optical system 204.Note that, in the case of requiring further accuracy, a distance betweenthe liquid crystal layer 216 of the reflection type spatial lightmodulator 203 and the principal point of the lens 241 a is desirably setto f1. However, as shown in FIG. 11, because the reflection type spatiallight modulator 203 is extremely thin and a distance between the liquidcrystal layer 216 and the glass plate 217 is extremely short, themagnitude of a change in its wavefront form between the liquid crystallayer 216 and the glass plate 217 as well is extremely low. Accordingly,to simplify, from the standpoint of the configuration of the reflectiontype spatial light modulator 203, a distance between a position at whicha focal distance is easily set (for example, the surface (in thevicinity of the surface) of the reflection type spatial light modulator203) and the lens 241 a may be set to f1, thereby making adjustmenteasy. In addition, in the case of requiring further accuracy, a distancebetween the primary point of the converging optical system 204 and theprimary point of the lens 241 b is desirably set to f2. However, theconverging optical system 204 is composed of a plurality of lenses,which makes it difficult to perform positioning at the primary points insome cases. In that case, to simplify, from the standpoint of theconfiguration of the converging optical system 204, a distance between aposition at which a focal distance is easily set (for example, thesurface (in the vicinity of the surface) of the converging opticalsystem 204) and the lens 241 b may be set to f2, thereby makingadjustment easy.

Further, a beam diameter of the laser light L is determined by a ratiobetween f1 and f2 (a beam diameter of the laser light L incident ontothe converging optical system 204 is f2/f1 times as long as the beamdiameter of the laser light L emitted from the reflection type spatiallight modulator 203). Accordingly, in both cases in which the laserlight L is a parallel light or a light having a small spread, it ispossible to acquire a desired beam diameter in the laser light Lincident onto the converging optical system 204 while keeping an angleof the laser light L emitted from the reflection type spatial lightmodulator 203.

As described above, it is possible to adjust a beam diameter and aspread angle of the laser light L by the adjustment optical system 240.In the laser working method for forming the modified region 7 serving asa starting point for cutting in the object 1, the condition forconverging light based on a spread angle or a beam diameter of the laserlight L is extremely important as compared with a laser working methodfor performing working from the surface in order to achieve precisecutting, and in some cases, the laser light L which is not a parallellight, but has a small spread angle (for example, approximately severalmrad to several tens of mrad) is necessary for the converging opticalsystem 204 in order to form the modified region 7 suitable for cuttingwith high precision. Therefore, in order to meet the basic workingconditions for forming the modified region 7 in the case in which thereflection type spatial light modulator 203 is installed and in the casein which the reflection type spatial light modulator 203 is notinstalled, it is necessary to set a beam diameter and a spread angle ofthe laser light L incident onto the converging optical system 204 (tothose in the case in which the reflection type spatial light modulator203 is not installed).

Then, by use of the adjustment optical system 240, it is possible toconverge the laser light L by the converging optical system 204 whilemaintaining the wavefront (aberration) modulated by the reflection typespatial light modulator 203, and it is possible to form a modifiedregion inside thereof with the laser light L having a predetermined beamdiameter and a predetermined spread angle. Thereby, it is possible toefficiently utilize an effective diameter of the converging opticalsystem 204 by the laser light L having a predetermined spread angle, andto form a precise modified region suitable for cutting.

Note that the lenses 241 a and 241 b of the adjustment optical system240 are preferably provided on the optical path of the laser light Lbetween the reflection type spatial light modulator 203 and thereflective member 208. The reason for that is as follows. That is, whena light having a large spread (a light between the lens 241 a and thelens 241 b) is made incident onto the plate-shaped reflective member 208and the beam splitters 209 and 210, spherical aberration or astigmatismis generated. Accordingly, when the lens 241 b is disposed at thesubsequent stage of the reflective member 208, a light emitted from thelens 241 a to have an angle to the optical axis is made incident ontothe reflective member 208 and the beam splitters 209 and 210, to bethereafter made incident onto the lens 241 b. Therefore, an accuracy ofthe laser light L incident onto the converging optical system 204 islowered under the effect of spherical aberration or astigmatism.Further, the adjustment optical system 240 is desirably equipped with amechanism that fine-adjusts the respective positions of the lenses 241 aand 241 b independently. Further, in order to effectively use aneffective area of the reflection type spatial light modulator 203, abeam expander may be provided on the optical path of the laser light Lbetween the reflection type spatial light modulator 203 and the laserlight source 202.

Next, as a manufacturing method of a laser working apparatus accordingto the present embodiment, a manufacturing method of the above-describedlaser working apparatus 200 will be described.

First, as shown in FIG. 12, a standard laser working apparatus 200 shaving a configuration substantially the same as that of theabove-described laser working apparatus 200 is prepared. The standardlaser working apparatus 200 s is a laser working apparatus capable offorming the modified region 7 with a high function as a starting pointfor cutting, and for example, a laser working apparatus in which anuncut portion has a predetermined percentage or less in the case inwhich the modified regions 7 are formed along a plurality of lines 5 setin a lattice pattern under a given condition and the object 1 is cut.

With respect to the standard laser working apparatus 200 s, a referencespherical mirror 221 is installed in place of the object 1 such that itsoptical axis matches the optical axis of a standard converging opticalsystem 204 s, and a wavefront measuring instrument 222 is installed inplace of the AF unit 212. Then, the wavefront of a standard laser lightLs emitted from the standard converging optical system 204 s of thestandard laser working apparatus 200 s is measured by the wavefrontmeasuring instrument 222, to acquire standard wavefront data. Note thatthe reference spherical mirror 221 is manufactured to an accuracy morethan the accuracy of the wavefront measuring instrument 222, and thus,distortion of the wavefront of the standard laser light Ls generated dueto the reflection of standard laser light Ls by the reference sphericalmirror 221 can be disregarded.

Next, as shown in FIG. 3, the laser working apparatus 200 before thefinal adjustment, which has the supporting base 201, the laser lightsource 202, the reflection type spatial light modulator 203, theconverging optical system 204, and the controller 205 is prepared.

With respect to the laser working apparatus 200, the reference sphericalmirror 221 is installed in place of the object 1 such that its opticalaxis matches the optical axis of the converging optical system 204, andthe wavefront measuring instrument 222 is installed in place of the AFunit 212. Then, the wavefront of the laser light L emitted from theconverging optical system 204 of the laser working apparatus 200 ismeasured by the wavefront measuring instrument 222, to acquire itswavefront data.

Next, a control signal for controlling the reflection type spatial lightmodulator 203 such that a wavefront of the laser light L becomes thewavefront of the standard laser light Ls is calculated on the basis ofthe standard wavefront data and the wavefront data, to be stored in thecontroller 205. In detail, the standard wavefront data and the wavefrontdata are acquired as Zernike polynomials, and a difference between theZernike polynomials of the standard wavefront data and the Zernikepolynomials of the wavefront data is determined, and a control signalthat makes up the difference is calculated, to be stored in thecontroller 205. For example, in the case in which the Zernikepolynomials of the standard wavefront data are “(1×the firstterm)+(4×the second term)+(4×the third term),” and the Zernikepolynomials of the wavefront data are “(1×the first term)+(2×the secondterm)+(4×the third term),” a control signal that further doubles thesecond term in the Zernike polynomials of the wavefront data iscalculated, to be stored in the controller 205.

Note that the reason that the wavefront measuring instrument 222 is notdirectly disposed on the emission side of the converging optical system204 to measure the wavefront of the laser light L is as follows. Thatis, in the case in which the modified region 7 serving as a startingpoint for cutting is formed by irradiating the plate-shaped object 1with the laser light L while locating the converging point P within theobject 1, the numerical aperture of the laser light L converged insidethe object 1 by the converging optical system 204 becomes, for example,0.55 to 0.80, that is extremely high. Therefore, the intensity of thelaser light L weakens or phase differences among the plurality of rayscomposing the laser light L exceed the measurement limit of thewavefront measuring instrument 222. This reason is also the same in thecase in which the wavefront of the standard laser light Ls is measuredin the standard laser working apparatus 200 s.

As described above, by preparing the laser working apparatus capable offorming the modified region 7 with a high function as a starting pointfor cutting as the standard laser working apparatus 200 s, it ispossible to make up an individual difference between the apparatuses,and to manufacture the laser working apparatus 200 having theperformance equivalent to that of the standard laser working apparatus200 s.

Next, as shown in FIG. 14, a reference planar mirror 223 is installedbetween the beam splitter 210 and the converging optical system 204 soas to be perpendicular to the optical axis of the laser light L in thelaser working apparatus 200. Then, the wavefront of the laser light Lreflected in sequence by the reference planar mirror 223 and the beamsplitter 210 is measured by the wavefront measuring instrument 222, toacquire its wavefront data as Zernike polynomials. Note that thereference planar mirror 223 is manufactured to an accuracy more than theaccuracy of the wavefront measuring instrument 222, and thus, distortionof the wavefront of the laser light L generated due to the reflection ofthe laser light L by the reference planar mirror 223 can be disregarded.

Next, as shown in FIG. 15, a reference wafer 224 with a predeterminedthickness composed of the same material as the object 1 is prepared, andthe reference wafer 224 is installed in the laser working apparatus 200such that the converging point P of the laser light L converged by theconverging optical system 204 is located on the rear face (laser lightemitting surface) of the reference wafer 224. Moreover, the referencespherical mirror 221 is installed on the emission side of the referencewafer 224 such that its optical axis matches the optical axis of theconverging optical system 204. Then, the wavefront of the laser light Lwhich is made transmissive in sequence through the converging opticalsystem 204 and the reference wafer 224, and is reflected by thereference spherical mirror 221 to be made transmissive in sequencethrough the reference wafer 224 and the converging optical system 204,and is reflected by the beam splitter 210, is measured by the wavefrontmeasuring instrument 222, to acquire the wavefront data as Zernikepolynomials. Note that the reference wafer 224 is manufactured to anaccuracy more than the accuracy of the wavefront measuring instrument222, and thus, distortion of the wavefront of the laser light Lgenerated due to the transmission of the laser light L through thereference wafer 224 can be disregarded.

Next, a difference between the Zernike polynomials of the wavefront dataacquired in the state of FIG. 14 and the Zernike polynomials of thewavefront data acquired in the state of FIG. 15 is determined. Thereby,it is possible to cancel the distortion of the wavefront even if thewavefront of the laser light L is distorted by the reflection thereof bythe beam splitter 210. Then, a control signal for controlling thereflection type spatial light modulator 203 such that a differencebetween the Zernike polynomials becomes a predetermined difference orless (that is, in the case in which the converging point P of the laserlight L is located at a predetermined distance (which is equal to apredetermined thickness of the reference wafer 224) from the front face3 of the object 1, the aberration of the laser light L generated at thatposition becomes a predetermined aberration or less), is calculated.

Note that if a difference between the Zernike polynomials is apredetermined difference or less, a control signal for controlling thereflection type spatial light modulator 203 is made unnecessary.Further, a control signal for controlling the reflection type spatiallight modulator 203 such that a difference between the Zernikepolynomials becomes substantially zero (that is, in the case in whichthe converging point P of the laser light L is located at apredetermined distance (which is equal to a predetermined thickness ofthe reference wafer 224) from the front face 3 of the object 1, theaberration of the laser light L generated at that position becomessubstantially zero), may be calculated.

The calculations for control signals for controlling the reflection typespatial light modulator 203 are executed, for example, while changingthe predetermined thickness of the reference wafer 224 gradually by 50μm from 50 μm to 700 μm. Then, the control signal for controlling thereflection type spatial light modulator 203 such that aberration of thelaser light L converged inside the object 1 becomes a predeterminedaberration or less (in other words, the wavefront of the laser light Lbecomes a predetermined wavefront inside the object 1), is stored in thecontroller 205 so as to be associated with a control signal forcontrolling the laser engine 230 including the converging optical system204 such that the converging point P of the laser light L is located ata predetermined distance from the front face 3 of the object 1.

Thereby, in the case in which the modified regions 7 are formed in aplurality of lines so as to line up in the thickness direction of theobject 1 with respect to one of the lines 5, aberration of the laserlight L converged inside the object 1 can be made to be a predeterminedaberration or less in accordance with each of the modified regions 7 ina plurality of lines to be formed (in other words, the wavefront of thelaser light L can be made to be a predetermined wavefront inside theobject 1).

Meanwhile, strictly speaking, the laser light L modulated (corrected) bythe reflection type spatial light modulators 203 and 203 s is changed inits wavefront form due to its propagation through space. In particular,in the case in which the laser light L emitted from the reflection typespatial light modulators 203 and 203 s or the laser light L incidentonto the converging optical systems 204 and 204 s is a light having apredetermined spread (i.e., a light other than a parallel light), thewavefront form at the reflection type spatial light modulators 203 and203 s and the wavefront form at the converging optical systems 204 and204 s do not match one another, and as a result, precise internalworking to be targeted may be interrupted. Therefore, it is necessary tomatch the wavefront form at the reflection type spatial light modulators203 and 203 s to the wavefront form at the converging optical systems204 and 204 s. Further, it is also important to match the wavefront format the converging optical systems 204 and 204 s to the wavefront form atthe wavefront measuring instrument 222, and to match the wavefront format the reflection type spatial light modulators 203 and 203 s to thewavefront form at the wavefront measuring instrument 22. For thatpurpose, it is more desirable that a change in its wavefront form whenthe laser light L propagates from the reflection type spatial lightmodulators 203 and 203 s to the converging optical systems 204 and 204 sis determined by measurement or the like, and wavefront shaping(aberration correction) pattern information taking into account thechange in the wavefront form is input to the reflection type spatiallight modulators.

Or, in order to match the wavefront form at the reflection type spatiallight modulators 203 and 203 s to the wavefront form at the convergingoptical systems 204 and 204 s, by providing adjustment optical systems240 and 250 as shown in FIGS. 24 to 27, it is possible to achieve moreaccurate wavefront shaping. The manufacturing method of the laserworking apparatus shown in FIGS. 24 to 27 is basically the same as themanufacturing method of the laser working apparatus shown in FIGS. 12 to15. The difference being in the point that there are the adjustmentoptical systems 240 and 250.

First, the adjustment optical system 240 has at least two lenses 241 aand 241 b. The lenses 241 a and 241 b are for matching the wavefrontform at the reflection type spatial light modulators 203 and 203 s tothe wavefront form at the converging optical systems 204 and 204 s insimilarity. The lenses 241 a and 241 b are disposed between thereflection type spatial light modulator 203 and the reflective member208 such that a distance between the reflection type spatial lightmodulator 203 and the lens 241 a becomes a focal length f1 of the lens241 a, a distance between the converging optical system 204 and the lens241 b becomes a focal length f2 of the lens 241 b, a distance betweenthe lens 241 a and the lens 241 b becomes f1+f2, and the lens 241 a andthe lens 241 b becomes a double telecentric optical system.

By disposing the lenses 241 a and 241 b in this way, even if the laserlight L has a small spread angle, it is possible to align the wavefrontform at the reflection type spatial light modulators 203 and 203 s tothe wavefront form at the converging optical systems 204 and 204 s.

A beam diameter of the laser light L is determined by a ratio between f1and f2 (a beam diameter of the laser light L incident onto theconverging optical systems 204 and 204 s is f2/f1 times as long as thebeam diameter of the laser light L emitted from the reflection typespatial light modulators 203 and 203 s). Accordingly, in both cases inwhich the laser light L is a parallel light or a light having a smallspread, it is possible to acquire a desired beam diameter in the laserlight L incident onto the converging optical systems 204 and 204 s whilekeeping an angle of the laser light L emitted from the reflection typespatial light modulators 203 and 203 s.

Further, the adjustment optical system 250 has at least two lenses 251 aand 251 b. The lenses 251 a and 251 b are for matching the wavefrontform at the converging optical systems 204 and 204 s or the referenceplanar mirror 223 and the wavefront form at the wavefront measuringinstrument 222 in similarity. Note that the disposition of theadjustment optical system 250 is based on the same technical idea forthe adjustment optical system 240. Further, the adjustment opticalsystems 240 and 250 are desirably equipped with mechanisms thatfine-adjust the respective positions of the lenses respectively providedthereto independently.

Next, as a laser working method according to the present embodiment, alaser working method carried out in the above-described laser workingapparatus 200 will be described.

First, the object 1 is prepared. The object 1 is, as shown in FIG. 16, asemiconductor substrate with a thickness of 300 μm, which is composed ofsilicon, for example. A plurality of function elements (not shown)arranged in a matrix state are generally formed in a direction parallelto and in a direction perpendicular to an orientation flat 6 on thefront face of the semiconductor substrate. Note that the functionelements are, for example, semiconductor operational layers formed bycrystal growth, light-receiving elements such as photodiodes or thelike, light-emitting elements such as laser diodes or the like, orcircuit elements formed as circuits, or the like.

Next, the object 1 is fixed on the supporting base 201 of the laserworking apparatus 200. Then, a plurality of lines 5 a extending in adirection parallel to the orientation flat 6 and a plurality of lines 5b extending in a direction perpendicular to the orientation flat 6 areset in a lattice pattern so as to pass between the adjacent functionelements. Here, the converging point P of the laser light L is made tobe located 270 μm, 210 μm, 150 μm, and 50 μm from the front face 3 ofthe object 1, to form the modified regions 7 including molten processedregions in four lines along the respective lines 5 a and 5 b so as toline up in the thickness direction of the object 1.

First, the controller 205 outputs a control signal for controlling theposition of the laser engine 230 including the converging optical system204, to control the laser engine 230 including the converging opticalsystem 204 such that the converging point P of the laser light L islocated 270 μm from the front face 3 of the object 1 as shown in FIG.17A. Then, the controller 205 controls the laser engine 230 includingthe converging optical system 204 such that the converging point P ofthe laser light L is relatively moved along one of the lines 5 a. At thesame time, the controller 205 outputs a control signal for controllingthe reflection type spatial light modulator 203, to control thereflection type spatial light modulator 203 such that aberration of thelaser light L converged inside the object 1 becomes a predeterminedaberration or less. Thereby, the modified region 7 ₁ serving as astarting point for cutting along the one of the lines 5 a is formed.

Note that the control signal for controlling the reflection type spatiallight modulator 203 is stored in the controller 205 so as to beassociated with the control signal for controlling the position of thelaser engine 230 including the converging optical system 204 such thatthe converging point P of the laser light L is located 270 μm from thefront face 3 of the object 1.

Next, the controller 205 outputs a control signal for controlling thelaser engine 230 including the converging optical system 204, to controlthe laser engine 230 including the converging optical system 204 suchthat the converging point P of the laser light L is located 210 μm fromthe front face 3 of the object 1 as shown in FIG. 17B. Then, thecontroller 205 controls the laser engine 230 including the convergingoptical system 204 such that the converging point P of the laser light Lis relatively moved along the same one line 5 a. At the same time, thecontroller 205 outputs a control signal for controlling the reflectiontype spatial light modulator 203, to control the reflection type spatiallight modulator 203 such that aberration of the laser light L convergedinside the object 1 becomes a predetermined aberration or less. Thereby,the modified region 7 ₂ serving as a starting point for cutting alongthe same one line 5 a is formed.

Note that the control signal for controlling the reflection type spatiallight modulator 203 is stored in the controller 205 so as to beassociated with the control signal for controlling the position of thelaser engine 230 including the converging optical system 204 such thatthe converging point P of the laser light L is located 210 μm from thefront face 3 of the object 1. Further, the direction in which theconverging point P of the laser light L is relatively moved along theline 5 a may be a direction opposite to that in the case of forming themodified region 7 ₁ in order to improve the speed of forming themodified region 7 ₂.

Next, the controller 205 outputs a control signal for controlling thelaser engine 230 including the converging optical system 204, to controlthe laser engine 230 including the converging optical system 204 suchthat the converging point P of the laser light L is located 150 μm fromthe front face 3 of the object 1 as shown in FIG. 18A. Then, thecontroller 205 controls the laser engine 230 including the convergingoptical system 204 such that the converging point P of the laser light Lis relatively moved along the same one line 5 a. At the same time, thecontroller 205 outputs a control signal for controlling the reflectiontype spatial light modulator 203, to control the reflection type spatiallight modulator 203 such that aberration of the laser light L convergedinside the object 1 becomes a predetermined aberration or less. Thereby,the modified region 7 ₃ serving as a starting point for cutting alongthe same one line 5 a is formed.

Note that the control signal for controlling the reflection type spatiallight modulator 203 is stored in the controller 205 so as to beassociated with the control signal for controlling the position of thelaser engine 230 including the converging optical system 204 such thatthe converging point P of the laser light L is located 150 μm from thefront face 3 of the object 1. Further, the direction in which theconverging point P of the laser light L is relatively moved along theline 5 a may be a direction opposite to that in the case of forming themodified region 7 ₂ in order to improve the speed of forming themodified region 7 ₃.

Next, the controller 205 outputs a control signal for controlling thelaser engine 230 including the converging optical system 204, to controlthe laser engine 230 including the converging optical system 204 suchthat the converging point P of the laser light L is located 50 μm fromthe front face 3 of the object 1 as shown in FIG. 18B. Then, thecontroller 205 controls the laser engine 230 including the convergingoptical system 204 such that the converging point P of the laser light Lis relatively moved along the same one line 5 a. At the same time, thecontroller 205 outputs a control signal for controlling the reflectiontype spatial light modulator 203, to control the reflection type spatiallight modulator 203 such that aberration of the laser light L convergedinside the object 1 becomes a predetermined aberration or less. Thereby,the modified region 7 ₄ serving as a starting point for cutting alongthe same one line 5 a is formed.

Note that the control signal for controlling the reflection type spatiallight modulator 203 is stored in the controller 205 so as to beassociated with the control signal for controlling the position of thelaser engine 230 including the converging optical system 204 such thatthe converging point P of the laser light L is located 50 μm from thefront face 3 of the object 1. Further, the direction in which theconverging point P of the laser light L is relatively moved along theline 5 a may be a direction opposite to that in the case of forming themodified region 7 ₃ in order to improve the speed of forming themodified region 7 ₄.

As described above, after the modified regions 7 ₁ to 7 ₄ in four linesare formed along the same one line 5 a, the modified regions 7 ₁ to 7 ₄in four lines are formed along another one of the lines 5 a. Then, afterthe modified regions 7 ₁ to 7 ₄ in four lines are formed along each ofall the lines 5 a, the modified regions 7 ₁ to 7 ₄ in four lines areformed along each of all the lines 5 b in the same way in the case inwhich the modified regions 7 ₁ to 7 ₄ are formed along the lines 5 a.

In this way, in the case in which the plurality of lines 5 are set withrespect to the object 1, provided that after the modified regions 7 in aplurality of lines are formed along one of the lines 5, the modifiedregions 7 in a plurality of lines are formed along another one of thelines 5, the following effect is brought about. That is, even in a casewhere there is undulation on the front face 3 of the object 1, in orderto focus the converging point P of the laser light L on a position at apredetermined distance from the front face 3 with high precision, the AFunit 212 acquires data on varying levels of the front face 3 along theline 5, to fine-adjust a distance between the converging optical system204 and the object 1 on the basis of the data on varying levels.Accordingly, provided that after the modified regions 7 in a pluralityof lines are formed along one of the lines 5, the modified regions 7 ina plurality of lines are formed along another one of the lines 5, it ispossible to decrease the number of switching data on varying levels, andit is possible to form the modified regions 7 in a plurality of linesalong the respective lines 5 at positions at predetermined distancesfrom the front face 3 of the object 1 with high precision.

As described above, in the laser working method according to the presentembodiment, the object 1 is irradiated with the laser light L modulatedby the reflection type spatial light modulator 203 such that aberrationof the laser light L converged inside the object 1 becomes apredetermined aberration or less (or, the wavefront of the laser light Lbecomes a predetermined wavefront inside the object 1). Therefore, theaberration of the laser light L generated at a position on which theconverging point P of the laser light L is located is made as small aspossible, to enhance the energy density of the laser light L at thatposition, which makes it possible to form the modified region 7 with ahigh function as a starting point for cutting. In addition, because thereflection type spatial light modulator 203 is used, it is possible toimprove the utilization efficiency of laser light L as compared with atransmissive type spatial light modulator. Such improvement of theutilization efficiency of the laser light L is particularly important inthe case in which the modified region 7 serving as a starting point forcutting is formed in the plate-shaped object 1. Accordingly, inaccordance with the laser working method according to the presentembodiment, it is possible to reliably form the modified region 7serving as a starting point for cutting. As a result, when a stress isapplied to the object 1 in which the modified region 7 is formed, via anexpand tape or the like, the modified region 7 sufficiently performs thefunction as a starting point for cutting. Therefore, it is possible tocut the object 1 along the line 5 with high precision, and to preventgeneration of an uncut portion.

The present invention is not limited to the above-described embodiment.

For example, in the above-described embodiment, after the modifiedregions 7 in a plurality of lines are formed along one of the lines 5,the modified regions 7 in a plurality of lines are formed along anotherone of the lines 5. However, the modified region 7 in another one linemay be formed along a plurality of lines 5 after the modified region 7in one line is formed along the plurality of lines 5.

In that case, the following effect is brought about. That is, in a casewhere the object 1 breaks by the formation of the modified regions 7 ina plurality of lines along one of the lines 5, if the modified regions 7in a plurality of lines are formed along another one of the lines 5after the modified regions 7 in a plurality of lines are formed alongone of the lines 5, the position of the object 1 is shifted by the breakof the object 1. Then, in order to form the modified regions 7 along thelines 5 with high precision, it is necessary to correct the position ofthe object 1. However, if the modified region 7 in another one line isformed along a plurality of lines 5 after the modified region 7 in oneline is formed along the plurality of lines 5, it is possible to preventthe position of the object 1 from being shifted by the break of theobject 1, and the number of corrections for the position of the object 1is decreased, which makes it possible to form the modified regions 7 ina plurality of lines along the plurality of lines 5 in a short time.

Further, at the time of forming modified regions 7 in one line or aplurality of lines including the modified region 7 farthest from thefront face 3 that is the laser light entrance surface of the object 1among the modified regions 7 in a plurality of lines, a distance betweenthe converging optical system 204 and the object 1 may be changed suchthat a distance between converging optical system 204 that converges thelaser light L inside the object 1 and the object 1 becomes apredetermined distance in accordance with the modified region 7 to beformed, and the laser light L may be modulated by the reflection typespatial light modulator 203 such that a wavefront of the laser light Lbecomes a predetermined wavefront inside the object 1 (or, aberration ofthe laser light L converged inside the object 1 becomes a predeterminedaberration or less).

The reason for that modulation of the laser light L by the reflectiontype spatial light modulator 203 is required at the time of forming themodified region 7 farthest from the front face 3 that is the laser lightentrance surface of the object 1 as described above, is because thefarther from the laser light entrance surface the position at which themodified region 7 is formed is, the larger the aberration of the laserlight L generated at the position on which the converging point P of thelaser light L is located is. That is, for example, in the case offorming the modified region 7 closest to the front face 3 that is thelaser light entrance surface of the object 1, when the aberration of thelaser light L converged inside the object 1 becomes a predeterminedaberration or less even if the laser light L is not modulated by thereflection type spatial light modulator 203, there is no need tomodulate the laser light L by the reflection type spatial lightmodulator 203. Thereby, it is possible to reliably form the modifiedregions 7 serving as starting points for cutting even in the case inwhich the modified regions 7 in a plurality of lines along one of thelines 5 is formed. Note that, in the case in which modulation of thelaser light L by the reflection type spatial light modulator 203 is notcarried out, the reflection type spatial light modulator 203 iscontrolled to be utilized as a normal reflecting mirror (that is,pattern information is used so as to be not input or in an OFF state).

Further, in place of movement of the laser engine 230, a movementmechanism that moves the supporting base 201 in the thickness directionof the object 1 may be provided to the supporting base 201. Further, theconverging optical system 204 may be moved in the thickness direction ofthe object 1 by utilizing the AF unit 212. Then, these may be combined.

Further, the reflection type spatial light modulator 203 and theadjustment optical system 240 as described above may be, as shown inFIG. 29, applied to the laser working apparatus 200 including an opticalpath length intergradation means 300 in place of the AF unit 212. Theoptical path length intergradation means 300 changes an optical pathlength between a lens 303 and a lens 304 by changing installing anglesof a plurality of deflecting mirrors 301 on the basis of a heightposition of the front face 3 of the object 1 detected by a heightposition detecting means (not shown), to change a position of theconverging point P of the laser light L converged by the convergingoptical system 204. This is because a distance to the position of theconverging point P of the laser light L converged by the convergingoptical system 204 is expressed by a function of an optical path lengthfrom the lens 303 to the lens 304. Note that, as a height positiondetecting means, for example, a means for detecting a height position ofthe front face 3 on the basis of a change in height position of thereflected light when the laser light L is made incident onto the frontface 3 of the object 1 at a predetermined incident angle, can be cited.

Further, as shown in FIG. 19, the laser working apparatus 200 may beequipped with the supporting base 201, the laser light source 202, aplurality of (here, two) reflection type spatial light modulators 203 aand 203 b that modulate the laser light L emitted from the laser lightsource 202, the converging optical system 204, and the controller 205.The controller 205 has a function of controlling the reflection typespatial light modulators 203 a and 203 b such that an opticalcharacteristic of the laser light L becomes a predetermined opticalcharacteristic. Note that, as shown in FIG. 20, because the tworeflection type spatial light modulators 203 a and 203 b are disposed soas to be equivalent to the disposition of lenses 403 a and 403 b of adouble telecentric optical system, it is possible to control its beamdiameter, its optical axis, or the like as an optical characteristic ofthe laser light L. Further, by at least one of the reflection typespatial light modulators 203 a and 203 b, it is also possible tomodulate the laser light L such that a wavefront of the laser light Lbecomes a predetermined wavefront inside the object 1 (or, aberration ofthe laser light L converged inside the object 1 becomes a predeterminedaberration or less).

In accordance with this laser working apparatus 200, because the laserworking apparatus 200 is equipped with the plurality of reflection typespatial light modulators 203 a and 203 b, it is possible to control itsbeam diameter, its optical axis, or the like as an opticalcharacteristic of the laser light L. Accordingly, even in the case inwhich the optical axis of the laser light L is shifted from any cause,it is possible to easily correct the shift, to reliably form themodified region 7 serving as a starting point for cutting.

At this time, as shown in FIG. 28, the adjustment optical system 240 maybe provided. The position at which the adjustment optical system 240 isdisposed differs depending on which of the reflection type spatial lightmodulators 203 a and 203 b is the wavefront controlled by. In the casein which the wavefront is controlled by the reflection type spatiallight modulator 203 a, the adjustment optical system 240 is disposedsuch that a distance between the reflection type spatial light modulator203 a and the lens 241 a becomes the focal distance f1. On the otherhand, in the case in which the wavefront is controlled by the reflectiontype spatial light modulator 203 b, the adjustment optical system 240 isdisposed such that a distance between the reflection type spatial lightmodulator 203 b and the lens 241 a becomes the focal distance f1. Then,in both cases, a distance between the lens 241 a and the lens 241 b isf1+f2, and a distance between the lens 241 b and the converging opticalsystem 204 is f2.

Further, at the time of forming the modified region 7, the laser light Lmay be modulated by the reflection type spatial light modulator 203 suchthat a numerical aperture of the laser light L converged inside theobject 1 becomes a predetermined numerical aperture. In this case, forexample, the modified region 7 with a high function as a starting pointfor cutting can be formed by changing the numerical aperture of thelaser light L according to a material of the object 1, a distance to aposition at which the modified region 7 must be formed, or the like.

Further, as shown in FIGS. 21 and 22, in the case in which the modifiedregions 7 serving as starting points for cutting are formed in at leastthree lines (here, three lines) along one of the lines 5 so as to lineup in the thickness direction of the object 1, the modified regions 7 ₁to 7 ₃ may be formed as follows.

First, as shown in FIG. 21A, the object 1 is irradiated with the laserlight L modulated by the reflection type spatial light modulator 203such that a numerical aperture of the laser light L converged inside theobject 1 is made relatively larger, to form the modified region 7 ₁farthest from the front face 3 that is the laser light entrance surfaceof the object 1 along the line 5.

Next, as shown in FIG. 21B, the object 1 is irradiated with the laserlight L modulated by the reflection type spatial light modulator 203such that a numerical aperture of the laser light L converged inside theobject 1 is made relatively smaller, to form the modified regions 7 ₂along the line 5.

Next, as shown in FIG. 22, the object 1 is irradiated with the laserlight L modulated by the reflection type spatial light modulator 203such that a numerical aperture of the laser light L converged inside theobject 1 is made relatively larger, to form the modified region 7 ₃closest to the front face 3 that is the laser light entrance surface ofthe object 1 along the line 5.

As described above, at the time of forming the modified region 7 ₂except for the modified region 7 ₁ farthest from the front face 3 thatis the laser light entrance surface of the object 1 and the modifiedregion 7 ₃ closest to the front face 3 among the modified regions 7 ₁ to7 ₃ in three lines, the laser light L is modulated by the reflectiontype spatial light modulator 203 such that a numerical aperture of thelaser light L converged inside the object 1 is made smaller as comparedwith the case in which the modified regions 7 ₁ and 7 ₃ are formed. Thatis, at the time of forming the modified region 7 ₁ farthest from thefront face 3 that is the laser light entrance surface of the object 1and the modified region 7 ₃ closest to the front face 3 as the modifiedregions 7 particularly important as starting points for cutting, theobject 1 is irradiated with the laser light L modulated by thereflection type spatial light modulator 203 such that a numericalaperture of the laser light L converged inside the object 1 is madelarger as compared with the case in which the modified region 7 ₂therebetween is formed.

Thereby, the modified region 7 ₁ farthest from the front face 3 that isthe laser light entrance surface of the object 1 and the modified region7 ₃ closest to the front face 3 can be made to be the modified regions 7with extremely high functions as starting points for cutting (forexample, the modified regions 7 including break). Further, the modifiedregion 7 ₂ therebetween is made to be the modified region 7 which isrelatively longer in the thickness direction of the object 1 (forexample, the modified region 7 including a molten processed region),which makes it possible to decrease the number of scans of the laserlight L along the line 5.

Note that, in the case in which the modified regions 7 are formed in aplurality of lines (for example, two lines) along the line 5 so as toline up in the thickness direction of the object 1, at the time offorming the modified regions 7 except for the modified region 7 closestto the front face 3 that is the laser light entrance surface of theobject 1 or a rear face 21 that is the opposed surface opposed to thelaser light entrance surface in the object 1 among the modified regions7 in plurality of lines, the laser light L is preferably modulated bythe reflection type spatial light modulator 203 such that a numericalaperture of the laser light L converged inside the object 1 is madesmaller as compared with the case in which the modified region 7 closestto the front face 3 or the rear face 21 is formed.

In this laser working method, at the time of forming the modified region7 closest to the front face 3 or the rear face 21 of the object as themodified region 7 particularly important as a starting point forcutting, the object 1 is irradiated with the laser light L modulated bythe reflection type spatial light modulator 203 such that a numericalaperture of the laser light L converged inside the object 1 is madelarger as compared with the case in which the other modified regions 7are formed. Therefore, the modified region closest to the front face 3or the rear face 21 of the object 1 can be made to be a modified regionwith an extremely high function as a starting point for cutting (forexample, the modified region including break).

Further, the converging point P of the laser light L may be located on aposition at a predetermined distance from the front face 3 that is thelaser light entrance surface of the object 1 by, not moving the laserengine 230 including the converging optical system 204 and thesupporting base 201, but modulating the laser light L by the reflectiontype spatial light modulator 203. In detail, in the case in which thelaser light L is converged at a position relatively deeper from thefront face 3 of the object 1, when the reflection type spatial lightmodulator 203 is controlled such that a spread angle of the laser lightL emitted from the reflection type spatial light modulator 203 to bemade incident onto the converging optical system 204 is made relativelysmaller, to converge the laser light L at a position relativelyshallower from the front face 3 of the object 1, it is recommended thatthe reflection type spatial light modulator 203 be controlled such thata spread angle of the laser light L emitted from the reflection typespatial light modulator 203 to be made incident onto the convergingoptical system 204 is made relatively larger.

Further, in the above-described embodiment, the wavefront data isacquired as Zernike polynomials. However, the embodiment is not limitedthereto. For example, the wavefront data may be acquired as Seidel'sclassification of aberrations, associated Legendre polynomials, or thelike.

Further, in the above-described embodiment, a control signal forcontrolling the reflection type spatial light modulator 203 such thataberration of the laser light L converged inside the object 1 becomes apredetermined aberration or less (or, the wavefront of the laser light Lbecomes a predetermined wavefront inside the object 1) is calculated onthe basis of an actual measurement, and may be calculated on the basisof a simulation or the like. It is a matter of course that the controlsignal may be stored in the controller 205 in the case in which acontrol signal is calculated on the basis of a simulation or the like.However, the control signal may be not stored in the controller 205, anda control signal may be calculated immediately before the modifiedregion 7 is formed.

Further, the object 1 is easily warped when its thickness reachesapproximately 20 μm. Therefore, in order to form the modified region 7at a position at a predetermined distance from the front face 3 that isthe laser light entrance surface of the object 1, the front face 3 ofthe object 1 is preferably pressed down toward the supporting base 201side with a laser light transmissive member such as a glass plate.However, in this case, aberration is generated under the effect of thelaser light transmissive member, which results in deterioration in theconverging power of the laser light L. Then, provided that the laserlight L is modulated by the reflection type spatial light modulator 203such that aberration of the laser light L converged inside the object 1becomes a predetermined aberration or less taking into account the laserlight transmissive member, it is possible to reliably form the modifiedregion 7 serving as a starting point for cutting.

Further, a laser light entrance surface at the time of forming themodified region 7 is not limited to the front face 3 of the object 1,but may be the rear face 21 of the object 1.

Further, in the above-described embodiment, the modified region 7including a molten processed region is formed inside the object 1composed of a semiconductor material. However, another type of themodified region 7 such as a crack region or a refractive index changedregion may be formed inside the object 1 composed of another materialsuch as glass or a piezoelectric material.

INDUSTRIAL APPLICABILITY

In accordance with the present invention, it is possible to reliablyform a modified region serving as a starting point for cutting.

The invention claimed is:
 1. A functional element chip forming method comprising the steps of: irradiating a plate-shaped substrate to be processed with a laser light; locating a converging point of the laser light within the substrate forming a functional element on its surface so as to form a modified region serving as a starting point for cutting along a line to cut the substrate, and that forms a functional element chip by cutting the substrate along the line to be cut, wherein a reflection spatial light modulator, which modulates the laser light, a converging optical system, which converges the laser light modulated by the reflection spatial light modulator inside the substrate, and an adjustment optical system, which has a first optical element and a second optical element functioning as lenses that are located on an optical path between the reflection spatial light modulator and the converging optical system, are provided; and disposing the first optical element and the second optical element so as to match a wavefront form at the reflection spatial light modulator to a wavefront form at the converging optical system, and so that the first optical element and the second optical element form a double telecentric optical system, wherein at the time of forming the modified region, the laser light is modulated by a reflection spatial light modulator such that aberration of the laser light occurs at a position on which a converging point of the laser light is located inside the substrate becomes a predetermined aberration or less.
 2. A functional element chip forming method including the steps of: irradiating a plate-shaped substrate to be processed with a laser light; locating a converging point of the laser light within the substrate forming a functional element on its surface so as to form a modified region serving as a starting point for cutting along a line to cut the substrate, and that forms a functional element chip by cutting the substrate along the line to be cut, wherein a reflection spatial light modulator, which modulates the laser light, a converging optical system, which converges the laser light modulated by the reflection spatial light modulator inside the substrate, and an adjustment optical system, which has a first optical element and a second optical element functioning as lenses that are located on an optical path between the reflection spatial light modulator and the converging optical system, are provided; and disposing the first optical element and the second optical element so as to match a wavefront form at the reflection spatial light modulator to a wavefront form at the converging optical system, and so that the first optical element and the second optical element form a double telecentric optical system, wherein at the time of forming the modified region, the laser light is modulated by a reflection spatial light modulator such that a wavefront of the laser light becomes a predetermined wavefront inside the substrate.
 3. The functional element chip forming method according to claim 1, wherein the first optical element and second optical element are disposed such that a distance between the reflection spatial light modulator and the first optical element becomes the first focal distance of the first optical element, a distance between the converging optical system and the second optical element becomes the second focal distance of the second optical element, and a distance between the first optical element the second optical element becomes the sum of the first focal distance and the second focal distance, which forms modified regions in a plurality of lines so as to line up in the thickness direction of the substrate along the line to cut of the substrate, wherein at the time of forming the modified regions in one line or a plurality of lines including a modified region farthest from a laser light entrance surface of the substrate among the modified regions in a plurality of lines, modifies the distance between the convergence optical system and the substrate so that the distance between the convergence optical system that converges the laser light inside the substrate and the substrate becomes a predetermined distance, in accordance with the modified region to be formed.
 4. The functional element chip forming method according to claim 2, wherein the first optical element and second optical element are disposed such that a distance between the reflection spatial light modulator and the first optical element becomes the first focal distance of the first optical element, a distance between the converging optical system and the second optical element becomes the second focal distance of the second optical element, and a distance between the first optical element the second optical element becomes the sum of the first focal distance and the second focal distance, which forms modified regions in a plurality of lines so as to line up in the thickness direction of the substrate along the line to cut of the substrate, wherein at the time of forming the modified regions in one line or a plurality of lines including a modified region farthest from a laser light entrance surface of the substrate among the modified regions in a plurality of lines, modifies the distance between the convergence optical system and the substrate so that the distance between the convergence optical system that converges the laser light inside the substrate and the substrate becomes a predetermined distance, in accordance with the modified region to be formed.
 5. The functional element chip forming method according to claim 3, wherein in the case in which the plurality of lines are set with respect to the substrate, the modified regions are formed in a plurality of lines along another one of the lines after forming the modified regions in a plurality of lines along one of the lines.
 6. The functional element chip forming method according to claim 4, wherein in the case in which the plurality of lines are set with respect to the substrate, the modified regions are formed in a plurality of lines along another one of the lines after forming the modified regions and a plurality of lines along one of the lines.
 7. The functional element chip forming method according to claim 3, wherein in the case in which the plurality of lines are set with respect to the substrate, the modified regions are formed in another one line along the plurality of lines after forming the modified regions in one line along the plurality of lines.
 8. The functional element chip forming method according to claim 4, wherein in the case in which the plurality of lines are set with respect to the substrate, the modified regions are formed in another one line along the plurality of lines after forming the modified regions in one line along the plurality of lines.
 9. The functional element chip forming method according to claim 1, wherein the substrate is a semiconductor substrate or a sapphire.
 10. The functional element chip forming method according to claim 2, wherein the substrate is a semiconductor substrate or a sapphire.
 11. The functional element chip forming method according to claim 3, wherein the substrate is a semiconductor substrate or a sapphire.
 12. The functional element chip forming method according to claim 4, wherein the substrate is a semiconductor substrate or a sapphire.
 13. The functional element chip forming method according to claim 7, wherein the substrate is a semiconductor substrate or a sapphire.
 14. The functional element chip forming method according to claim 6, wherein the substrate is a semiconductor substrate or a sapphire.
 15. The functional element chip forming method according to claim 7, wherein the substrate is a semiconductor substrate or a sapphire.
 16. The functional element chip forming method according to claim 8, wherein the substrate is a semiconductor substrate or a sapphire. 